Issues with PolymerTemplate in OSGi Environmnet

Hi folks,

currently I try to migrate an existing (Spring) based Vaadin Flow Application to OSGi and it seems like there is an issue with using PolymerTemplate in OSGi, generally.
I uploaded a Demo Project and a detailed description in my public github here: https://github.com/JulianFeinauer/vaadin-flow-karaf-example/issues/1

I would really appreciate every help here!

Thanks!
Julian